1. Field of the Invention
The present invention relates to foam detectors and, more particularly, to foam detectors used in conjunction with a concentrator for gas chromatographs.
2. Brief Description of the Prior Art
When a gas is diffused through a fluid, bubbles can form and collect on a surface layer of the fluid. The accumulation of bubbles is commonly referred to as foam.
In some applications, such as in gas chromatography sample preparation, sample vessels are used to extract volatile organics from water samples or the like. A pressurized sparging gas is introduced into the water sample and diffuses through the water sample. The volatile organics are carried out of the water sample by the sparging gas and concentrated by a trap in a sample concentrator. The concentrated organics are then released from the trap and passed to an analyzing instrument, such as a gas chromatograph. If the bubbling action of the sparging gas creates foam over the surface layer of the water sample, the foam may or may not be contained or dissipated by a bubble breaker defined by the sample vessel. The presence of foam can lead to erroneous measurements or contamination of the sample concentrator. U.S. Pat. No. 4,910,996 to Pfisterer et al. discusses foaming problems in gas chromatographs used in beer processing. To combat the foam problem, the Pfisterer patent discloses using pressure regulators to pressurize a beer sample and prevent outgassing of the beer. However, if outgassing does occur, there is no way to test for the presence of the foam prior to the advancement of the concentrated prepared sample into internal tubing housed within the sample concentrator or the gas chromatograph.
Another problem not addressed by the prior art is the process of cleaning the sample concentrator if inadvertent contamination of the internal tubing does occur. Cleaning a contaminated sample concentrator generally takes a few weeks and includes the steps of taking the contaminated sample concentrator offline, shipping the sample concentrator to a cleaning facility, and reinstalling the cleaned sample concentrator.
To help obviate the disadvantages of the prior art, the present invention generally includes a device for detecting the presence of foam positioned adjacent to a surface layer of a fluid. The device generally includes a first lead positioned adjacent to the surface layer of the fluid, a second lead positioned adjacent to the surface layer of the fluid and spaced apart or electrically insulated from the first lead, and a controller connected to the first lead and the second lead. The first lead and the second lead may be thermocouples, with the first lead spaced at a further linear distance from the surface layer of the fluid than the second lead. Alternatively, the first lead and the second lead may be made from an electrically conductive material.
A method for the detection of foam positioned adjacent to a surface layer of a fluid is also provided. The method generally includes the steps of positioning a pair of leads adjacent to the surface layer of the fluid, with the leads each spaced apart or electrically insulated from one another. Additional steps include forming foam on the surface layer of the fluid, bringing the foam in physical contact with one or both of the pair of leads after the step of forming foam on the surface of the fluid, and registering a presence of the foam. Still further steps include (1) reducing the temperature of one of the leads after the step of bringing the foam in physical contact with one of the pair of leads and (2) flowing an electrical current from one of the pair of leads, through the foam, to another of the pair of leads, after the step of bringing the foam in physical contact with both of the pair of leads.
One particular application of the present invention is a system for detecting the presence of foam in gas chromatography. The system generally includes a gas chromatograph, a sample concentrator, such as a modular sample concentrator fluidly connected to the gas chromatograph, a sample vessel defining an internal cavity fluidly connected to the, sample concentrator, a pair of leads positioned in the internal cavity of the sample vessel, and a controller connected to the pair of leads. A fluid and foam may also be included, the fluid contained in the internal cavity of the sample vessel and the foam positioned on a surface layer of the fluid, wherein the foam physically touches at least one of the pair of leads. The modular sample concentrator may generally include a first body section housing, internal tubing, and a second body section housing control electronics, wherein the first body section and the second body section are removably connected to one another. Cleaning the sample concentrator includes the steps of removing a contaminated first body section from a second body section, replacing the contaminated first body section with a clean first body section, and resuming operation of the sample concentrator.
The present invention allows foam to be detected by one or both of the pair of leads, through the controller, and alert the operator so that the system can be shut down or continue to operate, depending on preprogram settings. Moreover, if the sample concentrator is contaminated by foam, the sample concentrator can be easily and quickly returned to operative service.
These and other advantages of the present invention will be clarified in the description of the preferred embodiments taken together with the attached drawings in which like reference numerals represent like elements throughout.